This week, I was at Microsoft's Turkey headquarters giving talks on Microsoft Web Stack three days in a row for Microsoft Summer School. It was a really good opportunity to give information to MSPs about latest Microsoft web technologies. During these three days, I shared a lot of code and resources to get up to speed on web and web services development. In this post, I will share the links to those resources and code repositories.

Sample Chat Application

First of all, I have a very simple and stupid real-time web application. The source code is also available on GitHub if you are interested in: RedisScaleOutSample. Guess what it is? Yes, you’re right. It’s a chat application :) I’m using SignalR 2.0.0-beta2 on this sample and here is how my hub looks like:

This’s a single machine scenario and if we want to move this application to multiple VMs, a Web Farm or whatever your choice of scaling out your application, you will see that your application misbehaving. The reason is very simple to understand actually. Let’s try to understand why.

Understanding the Need of Backplane

Assume that you have two VMs for your super chat application: VM-1 and VM-2. The client-a comes to your application and your load balancer routes that request to VM-1. As your SignalR connection will be persisted as long as it can be, you will be connected to VM-1 for any messages you receive (assuming you are not on Long Pooling transport) and send (if you are on Web Sockets). Then, client-b comes to your application and the load balancer routes that request to VM-2 this time. What happens now? Any messages that client-a sends will not be received by client-b because they are on different nodes and SignalR has no idea about any other node except that it’s executing on.

To demonstrate this scenario easily in our development environment, I will fire up the same application in different ports through IIS Express with the following script:

I’m running IIS Express here from the command line and it’s a very powerful feature if you ask me. When you execute the following script (which is run.ps1 in my sample application), you will have the chat application running on localhost:9090 and localhost:9091:

When we try to same scenario now by connecting both endpoints, you will see that it’s not working as it should be:

SignalR makes it really easy to solve this type of problems. In its core architecture, SignalR uses a pub/sub mechanism to broadcast the messages. Every message in SignalR goes through the message bus and by default, SignalR uses Microsoft.AspNet.SignalR.Messaging.MessageBus which implements IMessageBus as its in-memory message bus. However, this’s fully replaceable and it’s where you need to plug your own message bus implementation for your scale out scenarios. SignalR team provides bunch of backplanes for you to work with but if you can totally implement your own if none of the scale-out providers that SignalR team is providing is not enough for you. For instance, the community has a RabbitMQ message bus implementation for SignalR: SignalR.RabbitMq.

Hooking up Redis Backplane to Your SignalR Application

In order to test configure using Redis as the backplane for SignalR, we need to have a Redis server up and running somewhere. The Redis project does not directly support Windows but Microsoft Open Tech provides the Redis Windows port which targets both x86 and x64 bit architectures. The better news is that they distribute the binaries through NuGet: http://nuget.org/packages/Redis-64.

Now I have Redis binaries, I can get the Redis server up. For our demonstration purposes, running the redis-server.exe without any arguments with the default configuration should be enough:

The parameters we are passing into the UseRedis method are related to your Redis server. For our case here, we don’t have any password and that’s why we passed string.Empty. Now, let’s compile the application and run the same PowerShell script now to stand up two endpoints which simulates a web farm scenario in your development environment. When we navigate the both endpoints, we will see that messages are broadcasted to all nodes no matter which node they arrive:

That was insanely easy to implement, isn’t it.

A Few Things to Keep in Mind

The purpose of the SignalR’s backplane approach is to enable you to serve more clients in cases where one server is becoming your bottleneck. As you can imagine, having a backplane for your SignalR application can affect the message throughput as your messages need to go through the backplane first and distributed from there to all subscribers. For high-frequency real-time applications, such as real-time games, a backplane is not recommended. For those cases, cleverer load balancers are what you would want. Damian Edwards has talked about SignalR and different scale out cases on his Build 2013 talk and I strongly recommend you to check that out if you are interested in.

A few days ago, I presented on a webcast about ASP.NET SignalR and real-time web application scenarios in Turkish and it went pretty great I think. I also managed to record the webcast successfully and put it on Vimeo.

During the day, I helped Jon by trying to be the dummy guy during his ASP.NET MVC presentation. I also presented on ASP.NET Web API and ASP.NET SignalR where I showed a few sample applications. You could find the source code for those samples on my GitHub repository: https://github.com/tugberkugurlu/IstanbulWebCamps201304.

I would like to thank Jon Galloway for coming to Istanbul for this event and allowing us to have such a fun day. I personally really enjoyed the whole event and also the small Istanbul tour I had with Jon I also would like to thank Brady Gaster as he's one of the people who made this event happen. I'm hoping that we will keep seeing these types of web events in Istanbul more

And it's now a real deal thanks to awesome Web Camps team! One leg of Microsoft Web Camps spring 2013 tour will be held in Microsoft Istanbul office on the 6th of April, 2013. It will be a full day event. Jon Galloway, Umit Sunar and me will be giving talks on various latest Microsoft Web Stack technologies including Windows Azure, ASP.NET Web API, ASP.NET SignalR, ASP.NET MVC and so on. You can see the typical agenda of Web Camps here.

You can also find more about Web Camps spring 2013 tour from Jon Galloway's and Brady Gaster's blog posts: